The invention is directed to a character generator for a non-mechanical printer and, in particular, for an electrophotographic printer.
WO-87/02162 already discloses a character generator for a non-mechanical printer. This character generator contains a plurality of light sources in an exposure line, these light sources, for example, being fashioned as light-emitting diodes. A latent, electrostatic image is generated on a transfer printing drum upon employment of the light sources. In such a character generator, all of the component parts forming the exposure line such as the light-emitting diodes, drive circuits and leads, can be firmly mounted on a common carrier, for-example can be glued. The carrier has a length that is at least as great as the width of the entire exposure line.
In such a character generator, it is not possible to replace a single defective component part, for example a single light-emitting diode, or an individual, integrated circuit without further ado. A character generator usually contains more than 100 component parts, so that all of the component parts that are still good must also be thrown away given the outage of one component part.
DE-C2-30 31 295 discloses an opto-electronic recording means wherein latent electrostatic images of a numerical characters to be printed are generated on a light-sensitive surface, for example of a photoconductive drum, via a light waveguide arrangement with the assistance of light-emitting diodes that are arranged in groups in mutually offset rows on screwed-down ceramic plates of a carrier element. The light waveguide arrangement is composed of a plurality of gradient fibers that are embedded such in a matrix material that a transmission of the image information arises due to the lens effect of the gradient fibers.
DE-A1-32 23 031 discloses a printer having an optical printer head for line-byline recording of graphics and text information, whereby light emission arrangements abutting one another via seating surfaces and having a plurality of light emission elements are arranged together with control elements on a carrier plate of ceramic and light points corresponding to the information to be recorded are imaged on a light-sensitive surface via an imaging optics. The light emission elements of the light emission arrangements that are preferably arranged in one row or graduated in two rows comprise light-emitting surfaces that are fashioned parallelogram-like in order to generate a faultless, quenchable latent electrostatic image on the light-sensitive surface. A cooling member that is connected to the carrier plate in thermally conductive fashion is also provided for eliminating the thermal energy of components arranged on the carrier plate. In a character generator fashioned in this way, it is likewise not possible without further ado to separately replace individually, malfunctioning light emission elements on the light emission arrangements without discarding the overall carrier plate.
U.S. Pat. No. 4,536,778 discloses a modularly constructed character generator of an electrophotographic printer means with which information are recorded line-by-line on a light-sensitive surface, for example of a photoconductive drum. A plurality of light-emitting modules are secured on a metal rail for this recording process. A respective, electrically and thermally conductive base plate on which a plurality of light-emitting chip elements is secured in an exposure line is typical of the individual modules. The length of every base plate is thereby preferably less than the length of the chip elements situated on the base plate. In order to form a uniform exposure line, the individual base plates having the light-emitting chip elements projecting beyond the limitation of the base plate are glued onto the metal rail in tight proximity. The projection of the chip elements beyond the base plate limitation has the disadvantage that the thin chip elements are damaged given improper handling of the modules. Over and above this, it is disadvantageous that the closely adjacent base plates may potentially expand to such an extent due to thermal stresses that appear given a high dissipated thermal power of the character generator or, respectively, of the light-emitting modules that the thin, light-emitting chip elements that project beyond the base plate limitation can break.